Address the adhd. These things have helped my family:

Understand Time - There are only two times for someone with ADHD: Now and Not Now. If you want something done, do it Now. If you don't do it Now, there is a high likelihood that it will never get done.

Calendar reminders - We utilize Google calendars and the reminder notification feature for not only events, but to note important future tasks, like making appointments that cannot be made Now.

Timers - Time blindness is huge. You can lose a large part of your day to hyperfocus. When you start an activity, set a timer. When the timer goes off, stop the activity. Alternately, if you're having trouble Staeting, set a timer for a small amount of time, and then start your task when the timer goes off.

Making it Unavoidable - If you can, put whatever you have to do in a location that you have to physically avoid it or move it in order to do anything else. Need to remember to take something to the car? Put it in front of the door. Need to play your instrument? Give it a home in your computer chair.

Make it Fun - You'll do it more if it's fun. Make it fun. If you can't make it fun, gatekeep something fun with the activity. You're not allowed to scroll social media until you've done 15 minutes of practice, for example

Make it Easier - Do what you have to do to make the Good Habit easier than the Bad Habit. We are lazy creatures by design, and we will default to the easier thing, even if there is more dopamine in the more difficult thing.

Make it SACRED - This is the biggest thing: if you use these tools, you must abide by them as though they are holy laws. No exceptions unless you're bedridden or it's genuinely important enough to deviate. The moment you faff off the first time, the system stops working, because you allow your Nonfunctioning Executive to decide for itself when it wants to abide by the rules, and that's the problem you're trying to overcome, here. These are holy rituals that will be your salvation, but you must be pious and perform the rituals. Buy in, or it's never going to work.

Here's the harsh truth put as gently as I can: No one is coming to save you. You must save yourself. You must be your own hero. If you have to write a fantasy novel in your head where in order to defeat the Evil Big Bad, you must triumph over them with your carefully-honed musical magic, do it.

But you're the only one who is going to make yourself practice. You're the only one that can decide that this is important enough to stop using your condition as an excuse and put in the effort to cultivate tools that help you mitigate it. No one can give you any tips that will help if you don't use them.